Magnetohydrodynamic generator



April 19, 1966 M. ROSNER 3,247,405

MAGNETOHYDRODYNAMIC GENERATOR Filed Nov. 21, 1961 INVENTOR Manfred Rosner BY W M WWXQ PM ATTORNEYS gEARGH Rm) United States Patent 3,247,405 MAGNETGHYDRODYNAMHQ GENERATOR Manfred Rosner, Wettingen, Aargau, Switzerland, as-

signor to Aktiengesellsehaft Brown, Boveri, dz Cie, Baden, Switzerland, a ioint-stock company Filed Nov. 21, 1961, Ser. No. 153,810 Claims priority, application Switzeriand, Dec. 13, 1960, 13,889/60 3 Claims. ((Jl. 310-11) This invention relates to magnetohydrodynamic generators for the production of electrical power. A magnetohydrodynamic generator is a device which includes a channel containing one or more pairs of spaced electrodes arranged transversely to the channel axis and means for establishing a magnetic field through the channel and spaced electrodes, also in a direction transverse to the channel axis. Hot ionized working gas is caused to flow at high velocity through the channel in an axial direction between the pairs of electrodes and magnetic field and causes an electrical potential to be produced at these electrodes. The ionization of the working gas can be augmented by admixing suitable substances therewith in order to obtain a higher electric conductivity which is most desirable.

Two general types of magnetohydrodynamic generators are known, namely, those operating on an open cycle and those operating on a closed cycle. With closed cycle operation, the working gas, together with the additive substance, is circulated in a closed path, the gas being heated, then passed through the channel containing the electrodes and magnetic field and then reheated prior to passing it once again through the channel. In such a system, obviously none of the working gas or additive is lost and hence, economic factors therefore play a minor part. In constructing such a closed-circuit generator system, one is therefore guided by physical and chemical viewpoints.

In order to avoid the danger of corrosion within the generator, which is particularly great at the high gas temperatures which are used, an inert gas is selected as the working gas, and this is preferably a rare gas known also as a noble gas. Theoretically, any element from the first to the third group of the periodic table can be used as the additive substance but the use of cesium is preferred because of its low ionization potential and also for other reasons. The disadvantage of a magnetohydrodynamic generator operating with a closed gaseous circuit is that the heat supply to the working gas must be effected by means of heat exchangers or by atomic energy at a very high temperature level and it is therefore technically difiicult to realize.

With an open cycle type of generator operation, new working gas is constantly produced by combustion and fed into the channel of the generator. The substance added to the working gas to raise its conductivity leaves the generator plant together with the waste working gases. The possibility that the additive is deposited on the postconneced heated exchangers has already been taken into consideration but the amounts of the additive recoverable in such manner are undoubtedly small. It is thus necessary to look for utmost economy in selection of the additive. This leads to use of potassium compounds which impart a high electrical conductivity to the working gas even in relatively low concentration. Other additives have not yet been suggested since either their unit cost is too high or they must be used in very large quantities, which frequently entails other disadvantages, in addition to the increase in cost. The obvious disadvantage of operating the generator on an open cycle is that the additives are lost, and they must therefore 3,247,405 Patented Apr. 19, 1966 be most sparingly, so that the degree of electrical conductivity achieved in the Working gas remains below the physically possible maximum.

The object of the present invention is to provide an improved gas plant arrangement for supplying an additive-supplemented hot working gas to the gas channel of a magnetohydrodynamic generator which combines the advantages of magnetohydrodynamic generators operating on closed and open cycles while, at the same time, avoiding the disadvantages inherent with each type of operation and which have already been explained. The objective of the invention is attained by means of a modified i.e. semi-open operating cycle which is essentially half closed and half open. The hot working gas operates on an open cycle in that it is discharged as waste to atmosphere after passing once through the gas channel of the generator. The additive to the working gas for increasing its. electrical conductivity operates on a closed cycle in that it is added to the hot working gas in advance of that part of the gas channel in which the electrodes and magnetic field producing components are located and recovered from the working gas thereafter for recirculation through the gas channel and generator.

One practical embodiment for the invention is shown in the accompanying drawings:

FIG. 1 is a schematic view of the improved generator system; and

FIG. 2 is a transverse section through the gas channel on line 22 of FIG. 1.

With reference now to the drawings, the magnethydrodynamic generator comprises an elongated tubular duct or channel 1 through which is passed a hot working gas 2 produced by combustion in a combustion chamber, not shown, and which is supplmented by an additive 3 that serves the purpose of ionizing the gas and hence, raising its electrical conductivity. The additive can be selected from any element from the first to the third group of the periodic table in any amount desired, and can be either in pure form or as part of a compound.

Located within channel 1 which may be established by a rectangularly configured duct are the other components essential to a generator of the magnetohydrodynamic type. These include the spaced electrode plates 4 located on one pair of opposite walls of the rectangular duct 1 and a magnetic field indicated by the letter H which passes through the other pair of opposite side walls of the duct and which has a direction transverse to the direction of flow of the hot working gas through the channel as shown in FIG. 2. During operation of the generator there occurs between electrode plates 4 a direct voltage E having a magnitude which depends, among other things, on the gas temperature, its velocity and ionization, and the strength of the magnetic field. After the Working gas 2 supplemented by the additive 3 passes through that part of the channel containing the electrodes 4 giving off energy, it is cooled as far as possible by downward flow through a heat exchanger 5 located in one vertical leg 6 of a U-shaped part of the channel. This heat exchanger can constitute a part of a steam turbine plant, for example, its steam generator, or it can be used for preheating the fuel and the combustion air for the magnetohydrodynamic generator itself, or it can be a component of any other useful system.

After the working gas and additive pass the heat exchanger 5, they flow upward through a gas washer 7 tocated in the other vertical leg 8 of the U-shaped channel portion. This gas washer can be a gas scrubbing plant of known design and the necessary wash water can be supplied through a spray nozzle indicated at 9. The additive which is thus separated from the working gas in 3 the gas Washer unit 7 accumulates as an aqueous solution in the sump 10 located at the lowest point of the U- shaped channel port-ion. The heat exchanger 5 is cleaned periodically by means of a spray nozzle 11 and this solution likewise accumulates in the sump 10. The working gas cleansed in the gas washer 7 of the additive is then permitted to escape to atmosphere through the outlet 12.

The wet gas purification which has been described has the advantage, compared to an electrical gas filter system, in that it utilizes the hygroscopic property of many additives. The approximately saturated solution of the additive 3 is liberated by simple filtration of combustion residues and other insoluble impurities in filter 1'4 and then fed again, as shown in FIG. 1 of the drawing, to the working gas in advance of the electrode plates 4 in through pipe 15 with the aid of pump-13. Introduction of the additive together with the fuel or the combustion .air in the combustion chamber which produces the hot working gas is also possible. A

By analogy to terminology used in'gas turbine engineering, the improved magnetohydrodynamic generator according to the invention thus can be said to operate on a semi-open cycle because the working gas is conducted in a single passage only through the gas channel of the generator and is then discharged as waste to the atmosphere, while the additive, after passing through the gas channel, is removed from the working gas by means of a gas scrubbing plant and thenadded once again to fresh working gas so that it, in effect, is recirculated over and over again in a closed cycle through the channel without appreciable loss. I

Due to the recovery of the additive, the unavoidable losses thereof are very small. Economical considerations thus play only a minor role, and any desired additive, all elements from the first to the third groups of the periodic system being suitable, can be used in any amount that is necessary to achieve the optimum electrical conductivity of the hot working gas. Both cesium compounds and potassium compounds which have been used exclusively prior to this invention, and which can now be employed in higher concentrations, can be used with the invent-ion, as well as other substances characterized by better corrosion properties. These latter have not been considered practical prior to this invention because their ionization potential is higher than that of cesium or potassium and hence, must be added to the working gas in larger quantities.

In conclusion, the improved magnetohydrodynamic generator operating on a semi-open cycle is similar in its design to the generator operating on an open cycle, but it also has the advantages of the generator operating on a closed cycle. In the selection of the additive substance, the cost problem is no longer of primary consideration. Both its physical and chemical properties can be utilized to a greater extent and the entire generator plant can be designed according to new points of view so that achievement of an optimum mode of operation becomes more nearly possible. The improved magnetohydrodynamic generator operating on the new semiopen cycle is thus not only equivalent to the closed and open cycle types but it also proves superior to them for the reasons which have been explained.

I claim:

1. In a magnetohydrodynamic generator for generation of electric power, the combination comprising a gas channel through which flows a high velocity hot working gas to which is added an element in pure form or as a compound selected from the first to the third group of the periodic table for ionizing the gas, spaced electrodes located in said channel for taking off the generated current, a magnetic field extending across said channel at said electrodes and transverse to the direction of gas fiow there-through, a gas cleansing unit located in a portion of said channel on the downstream side of said electrodes and magnetic field for removing said added element, a collecting device located at the lowest point of said channel for collecting the element removed from the working gas, and means returning the element from said collecting device to fresh hot working gas at the upstream side of said electrodes and magnetic field, said working gas being discharged as waste after leaving said cleansing unit.

. 2;. In a magnetohydrodynamic generator for generation of electric power, the combination comprising -a gas channel through which flows a high velocity hot working gas to which is added an element in pure form or as a compound selected from the first to the third group of the periodic table for ionizing the gas, spaced electrodes located in said channel for taking off the generated current, a magnetic field extending across said channel at said electrodes and transverse to the direction of gas flow therethrough, a gas cleansing unit located in a portion of said channel on the downstream side of said electrodes and magnetic field for removing said added element, and a gas cooling device placed in the flow path of said working gas following said electrodes and magnetic field and in advance of said gas cleansing unit, said working gas being discharged as waste after leaving said gas cleansing unit.

3. In a magnetohydrodynamic generator for generating electric power, the combination comprising a gas channel through which fiowsa high velocity hot working gas to which is added an element having hygroscopic properties, said element being in pure form or as a compound selected from the first to the third group of the periodic table for ionizing the gas, spaced electrodes located in said channel for taking off the generated current, a magnetic field extending across said channel at said electrodes and transverse to the direction of gas flow therethrough, a gas washer unit located in a portion of said channel on the downstream side of said electrodes and magnetic field for removing said added hygroscopic element, and a gas cooling device placed in the flow path of said working gas following said electrodes and magnetic field and in advance of said gas washer unit, said working gas being discharged as waste after leaving said gas washer unit.

References Cited by the Examiner UNITED STATES PATENTS 1,717,413 6/1929 Rudenberg 31011 3,155,850 11/1964 Meyer 31011 OTHER REFERENCES Power, November 1959, Design and Equipment Section, pages 62 and 64.

Publication: Magnetohydrodynamic Generators by Way, Westinghouse Engineer, July 1960, pages 105, 106 and 107.

ORIS L. RADER, Primary Examiner.

MILTON O. HIRSH-FIELD, DAVID X. SLINEY,

Examiners. 

1. IN A MAGNETOHYDRODYNAMIC GENERATOR FOR GENERATION OF ELECTRIC POWER, THE COMBINATION COMPRISING A GAS CHANNEL THROUGH WHICH FLOWS A HIGH VELOCITY HOT WORKING GAS TO WHICH IS ADDED AN ELEMENT IN PURE FORM OR AS A COMPOUND SELECTED FROM THE FIRST TO THE THIRD GROUP OF THE PERIODIC TABLE FOR IONIZING THE GAS, SPACED ELECTRODES LOCATED IN SAID CHANNEL FOR TAKING OFF THE GENERATED CURRENT, A MAGNETIC FIELD EXTENDING ACROSS SAID CHANNEL AT SAID ELECTRODES AND TRANSVERSE TO THE DIRECTION OF GAS FLOW THERETHROUGH, A GAS CLEANSING UNIT LOCATED IN A PORTION OF SAID CHANNEL ON THE DOWNSTREAM SIDE OF SAID ELECTRODES AND MAGNETIC FIELD FOR REMOVING SAID ADDED ELEMENT, A COLLECTING DEVICE LOCATED AT THE LOWEST POINT OF SAID CHANNEL FOR COLLECTING THE ELEMENT REMOVED FROM THE WORKING GAS, AND MEANS RETURNING THE ELEMENT FROM SAID COLLECTING DEVICE TO FRESH HOT WORKING GAS AT THE UPSTREAM SIDE OF SAID ELECTRODES AND MAGNETIC FIELD, SAID WORKING GAS BEING DISCHARGED AS WASTE AFTER LEAVING SAID CLEANSING UNIT. 